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Viral Epidemiology: Basics
• Incidence2 is a measure of the number of new cases of a characteristic that develop in a population in a specified time period; whereas prevalence is the proportion of a population who have a specific characteristic in a given time period, regardless of when they first developed the characteristic.
• Researchers may study incident (new) cases of illnesses to help identify causes and prevent additional cases. Incidence is often reported for infectious diseases.
Viral Epidemiology: Technology in detecting & Monitoring
• Technologic13 changes that increased capacity for detecting, diagnosing, and monitoring infectious diseases included development early in the century of serologic testing and more recently the development of molecular assays based on nucleic acid and antibody probes. The use of computers and electronic forms of communication enhanced the ability to gather, analyze, and disseminate disease surveillance data.
• Serologic Testing: Serologic testing came into use in the 1910s and has become a basic tool to diagnose and control many infectious diseases.
• Viral Isolation and Tissue Culture: The first virus isolation techniques came into use at the turn of the century. They involved straining infected material through successively smaller sieves and inoculating test animals or plants to show the purified substance retained disease‐causing activity. The first "filtered" viruses were tobacco mosaic virus (1882) and foot‐ and‐mouth disease virus of cattle (1898). The U.S. Army Command under Walter Reed filtered yellow fever virus in 1900. The subsequent development of cell culture in the 1930s paved the way for large‐scale production of live or heat‐killed viral vaccines. Negative staining techniques for visualizing viruses under the electron microscope were available by the early 1960s.
• Molecular Techniques: During the last quarter of the 20th century, molecular biology has provided powerful new tools to detect and characterize infectious pathogens. The use of nucleic acid hybridization and sequencing techniques has made it possible to characterize the causative agents of previously unknown diseases (e.g., hepatitis C, human ehrlichiosis, hantavirus pulmonary syndrome, acquired immunodeficiency syndrome [AIDS], and Nipah virus disease).
• Molecular tools have enhanced capacity to track the transmission of new threats and find new ways to prevent and treat them. Had AIDS emerged 100 years ago, when laboratory‐based diagnostic methods were in their infancy, the disease might have remained a mysterious syndrome for many decades. Moreover, the drugs used to treat HIV‐infected persons and prevent perinatal transmission (e.g., replication analogs and protease inhibitors) were developed based on a modern understanding of retroviral replication at the molecular level.
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